Under circumstances where subsurface production formations have insufficient driving fluid for the purpose of forcing the production fluid to the surface of the earth, it is necessary to lift the production fluid to the surface by other suitable means. For example, pump systems are employed in many cases for the purpose of pumping the fluid to the surface and forcing it into flow lines or into other receiving means where it is subjected to preliminary treatment and then transmitted by means of pipelines and the like to other liquid handling facilities. Another method of producing liquid from wells of this nature involves a procedure generally known as gas-lift where a string of production fluid extending from the surface to the zone of interest is provided with a plurality of gas-lift valves positioned at spaced intervals along the length of the tubing. Gas is injected from an annulus between the tubing and well pipe through the gas-lift valves and into the tubing for the purpose of forcing liquid upwardly to the surface and ultimately into a flowline that is connected with the production tubing. Gas-lift systems for liquid production are quite expensive due to the cumulative expense of the number of gas-lift valves that are ordinarily necessary for each well. Moreover, each of the gas-lift valves must be preset for operation at differing pressures because of the vertical spacing thereof within the tubing string and because the valves must function in an interrelated manner to achieving lifting of liquid within the tubing string. It is desirable, therefore, to provide a system for gas-induced production of liquid from wells which achieves optimum production of the liquid without requiring exceptionally expensive equipment for the purpose of accomplishing such production.
Under certain circumstances, it may be desirable to inject a lubricant material into gas such as air being injected into a well for gas-lift induced liquid production. It is desirable, therefore, to provide apparatus for production of liquid from subsurface well formations which incorporates means for selective injection of lubricant material into the injected gas. It may also be desirable to provide for injection of chemical material into the discharge of a tubing string for the purpose of enhancing treatment of produced fluid as it flows toward handling or treatment facilities.